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Probing the E0 transitions in 186Pb using the SAGE spectrometer Date: 05.08-12.08/2013, 02.09-09.09.2013 Nucleus:186Pb Beam (charge state): 83Kr (15+) for 355MeV and 365MeV, 83Kr (16+) for 375MeV Target (thickness): 106Pd (1 mg/cm2) Beam energy: 355MeV, 365MeV and 375MeV (It changed depending on carbon foil unit used) Beam intensity: Typically 40-60enA Beam hours delivered roughly: 168 Instrumentation: SAGE/RITU/GREAT RITU dipole setting: 1st Part: First 6300 (SKI 94.5), then 6400 (SKI 90.4), then 6350 (SKI 92), 2nd Part: First 6400, then 6350 (SKI 94.5) RITU gas pressure: 0.7mbar SAGE coil current: 800A SAGE HV setting: 35kV Study of triple-shape coexistence in 186Pb employing in-beam γ-ray – conversion electron spectroscopy. Investigation of the low-lying 0+ states de-exciting via E0 transitions. In addition, investigation of the converted interband (oblate to prolate) transitions.
Across the physics disciplines, the 186Pb nucleus is the only known system, where the two first excited states, together with the ground state, form a triplet of zero-spin states assigned with prolate, oblate and spherical shapes. Here we report on a precision measurement where the properties of collective transitions in 186Pb were determined in a simultaneous in-beam γ-ray and electron spectroscopy experiment employing the recoil-decay tagging technique. The feeding of the 0+2 state and the interband 2+2→2+1 transition have been observed. We also present direct measurement of the energies of the electric monopole transitions from the excited 0+ states to the 0+ ground state. In contrast to the earlier understanding, the obtained reduced transition probability B(E2;2+1→0+2) value of 190(80) W.u., the transitional quadrupole moment |Qt(2+1→0+2)|=7.7(33) eb and intensity balance arguments provide evidence to reassign the 0+2 and 0+3 states with predominantly prolate and oblate shape, respectively. Our work demonstrates a step-up in experimental sensitivity and paves the way for systematic studies of electric monopole transitions in this region. These electric monopole transitions probe the nuclear volume in a unique manner and provide unexploited input for development of the next-generation energy density functional models.
High-spin states in the N = 128 nucleus 218Th have been investigated following fusion-evaporation reactions, using the recoil-decay tagging technique. Due to the short-lived nature of the ground state of 218Th prompt γ rays have been correlated with the α decay of the daughter nucleus 214Ra. The level scheme representing the decay of excited states has been extended to (16+) with the observation of six previously unreported transitions. The observations are compared with the results of shell model calculations and within the context of the systematics of neighbouring nuclei.